1. Field of the Invention
The present invention relates to a solid-state imaging device used for a digital camera and for a digital camera built in a mobile phone. In particular, the present invention relates to a MOS solid-state imaging device.
2. Description of the Related Art
A solid-state imaging device such as a CMOS sensor is, as of today, used for various purposes, that is, for a digital still camera, a digital video movie, and a monitor camera. In the solid-state imaging device, a photodiode is used as a photoelectric conversion element of a pixel. A read circuit is used to read a signal charge from the photodiode. In general, the read circuit includes 3 to 4 MOS transistors per pixel. Therefore, if the pixel size is reduced to make a pixel finer, an area occupied by the photodiode decreases, and thus, the number of saturation electrons for each pixel is reduced. Considering the foregoing circumstances, it is desired to provide a solid-state imaging device, which can prevent a reduction of the number of saturation electrons for each pixel even if the pixel size is reduced.